The UN's nuclear watchdog agency said on May 31 that Iran has failed to explain traces of uranium found at several undeclared sites and that it continues to breach enrichment limits spelled out in the 2015 nuclear agreement with world powers.
The news, outlined in two separate reports by the International Atomic Energy Agency (IAEA), could complicate talks currently under way in Vienna to revive the deal.
One report by IAEA Director-General Rafael Grossi said that Tehran has failed to provide “the necessary explanation for the presence of the nuclear material particles at any of the three locations where the agency has conducted complementary accesses [inspections]."
Most of the activity in question dates back to the early 2000s, before the Iran nuclear agreement, and has long been a center of inquiry about Iran's past nuclear program.
Another report estimated Iran's stockpile of enriched uranium at 3,241 kilograms, or around 16 times the limit set out in the 2015 deal with world powers.
Of that stockpile, it said Iran has produced 62.8 kilograms of uranium enriched up to 20 percent purity and 2.4 kilograms enriched up to 60 percent purity.
Under the nuclear deal, Iran is allowed to enrich uranium up to 3.67 percent purity, far below the 90 percent purity needed for a nuclear weapon.
"Sixty percent is almost weapons grade," Grossi told the Financial Times.
The IAEA hasn't been able to access data important to monitoring Iran's nuclear program since late February when Tehran started restricting international inspections of its facilities, according to the Vienna-based organization.
The IAEA and Iran earlier acknowledged the restrictions limited access to surveillance cameras at Iranian facilities, but the report issued on May 31 indicated they went much further.
Iran started limiting inspections in a bid to put pressure on the government of U.S. President Joe Biden to lift crippling sanctions reimposed after then-President Donald Trump pulled out of the 2015 nuclear deal with Iran unilaterally in 2018.
Since the U.S. withdrawal from the pact, Iran has been steadily violating its various restrictions, including on the types of centrifuges it's allowed to use, the amount of enriched uranium it is allowed to stockpile, and the purity to which it is allowed to enrich.